One method to control an electronic intake throttle of an internal combustion engine is to move the throttle plate from a closed position at key-on to a partially open position. Opening the throttle from a closed position allows more air to enter the engine during engine cranking and run-up. Opening the throttle also allows an engine controller to adjust engine fuel so that engine torque is increased without having to run the engine rich of stoichiometry. During a start, throttle position can also be adjusted in relation to time so that the engine air amount can be varied as the engine warms up.
The above-mentioned method can also have several disadvantages. For example, engine air flow is adjusted in response to the amount of time since start rather than in response to physical engine conditions. In other words, time since start is used to adjust the throttle as a surrogate for knowledge of actual engine operating conditions. As a result, starting emissions and intake manifold pressure control can vary more than is desired.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method of controlling intake valve timing that offers substantial improvements.